Chromosomes of Thaliaceans

SUMMARYThe chromosomes of six species of thaliaceans have been examined. The haploid number 11 was determined for Pyrosoma atlanticum and Doliolum denticolatum; the haploid number 12 was found for Pegea confoederata, Salpa fusiformis, Thalia democratica; the haploid number 13 was found in Salpa maxima.Salpa fusiformis and Thalia democratica are strikingly akin with respect to both number and morphology of diakinetic chromosomes whereas the other species of Salpida all possess distinguishing peculiarities. Pegea confoederata takes a place apart among the thaliaceans by virtue of the minute dimension of its chromosomes.The karyology of thaliaceans appears to be well differenciated from that of other tunicates and, although ascidians and thaliaceans are the most akin to each other, it is not possible to establish a meaningful probable relationship between their chromosomes